Dengue emerged as a serious health problem in the tropical Americas late in the 20th century following the resurgence of Aedes aegypti and the failure of an earlier eradication campaign to quash this invasive vector species. In the 1980s a second dengue vector, Aedes albopictus, invaded both Brazil and the USA and spread broadly in both countries. Research of the parent (2R01 AI44793) grant demonstrated that larval competition with A. albopictus caused displacement of A. aegypti in the southern USA, and that the same displacement mechanism operated between these two species in Brazil. The parent grant further showed that effects of larval competition are also manifested in the competency of emerged adults to vector arboviruses in the laboratory, stressed Aedes females being more susceptible to infection with and dissemination of dengue virus. A central goal of this project, which is more narrowly focused than a previous submission with Brazilian collaborators C. Codego and R. Lourengo-de- Oliveira of the Oswaldo Cruz Foundation, is to measure and understand the impact of larval competition on dengue transmission in Rio de Janeiro. Three specific research aims are complemented by a winter course to strengthen research capacity at the Foundation by training Brazilian students in the design and analysis of experiments related to vector ecology and disease epidemiology. Aim #1 evaluates the impact of larval competition in dengue-endemic areas of Rio de Janeiro, derives a surrogate measure of competition based on body size, and tests for effects of competition on adult longevity, another important variable affecting pathogen transmission. Aim #2 investigates whether competitive effects on dengue transmission can be detected in nature through measurements of adult body size related to dengue infection and dissemination rates among Aedes spp. field-collected during epidemic periods in Rio. The species-specific importance of transovarian transmission is also tested by assaying field- collected Aedes spp. males for dengue. Aim #3 incorporates new findings of the previous two aims with other, epidemiologically important vector and host variables into risk models for dengue transmission which will be publicly accessible on websites. The project will enhance understanding of the current ecology of the two invasive vector species in Brazil and their roles in dengue transmission, as well as strengthen the research potential of the largest tropical disease institute in the Americas. Dengue fever is currently the most prevalent and problematic arboviral disease vectored by mosquitoes and a serious public health concern in subtropical and tropical USA, such as south Texas, Hawaii, and Puerto Rico. This project investigates linkages between vector competence for dengue in Brazil and mosquito larval ecology, and strengthens the research capacity of collaborators in Rio de Janeiro, where dengue epidemics occur regularly.